This invention relates to joint prosthesis particularly adapted for replacing a joint between two of the long bones of the hand such as the joint between the metacarpal and the first phalanx that articulates with the metacarpal.
The joints between elongated bones of the hand can be damaged by accident or by diseases such as rheumatoid arthritis and osteoarthritis and often need to be surgically replaced. Past procedures for replacing damaged or diseased joints often have involved surgical removal of substantial portions of the bone adjacent a joint's articulating surfaces and implantation of an articulating prosthesis. The surgical procedure often involved removing not only substantial portions of bone but also of soft tissue attachments between the bony ends of the joint. This, in turn, has often required that the articulating ends of the prosthesis be fastened together in such a manner that they are not readily separated. Limited pivoting of the joint in the lateral direction (that is, in the radial/ulnar direction) was permitted in most prostheses of this kind. A finger joint of this general type as shown in Steffee, U.S. Pat. No. 4,001,603 is referred to as a `constrained hinged` prosthesis.
Other finger joint prosthesis are provided with stems having articulating, opposed heads and in which the heads were permitted lateral pivoting movement with respect to one another. One such prosthesis is shown in White, U.S. Pat. No. 4,242,759. The completely separable articulating heads described in the White patent contained mating ridges and troughs, the contact between the ridges and troughs varying with flexure of the joint. Lippincott U.S. Pat. No. 5,405,401 shows the use of lateral articulating surfaces to restrain the lateral pivoting movement.
It is known that certain arthritis diseases, such as rheumatoid arthritis, can cause severe radial/ulnar cosmetic deformity in the hand. Unfortunately, use of a `non-constrained` prosthesis design for patients with rheumatoid arthritis would allow postoperative return of severe deformity within joint replacements of the hand. This severe deformity in this type of a non-constrained type of implant could also lead to subluxation or complete dislocation of the two opposed head members resulting in failure of the implant device.
It is desired to provide a prosthesis so configured and arranged that its surgical implantation would not involve substantial disruption of soft tissue connections between the articulating bones nor removal of substantial portions of the bones themselves. Such prostheses would also control the possible return of cosmetic deformity to the hand. Desirably, such prostheses would duplicate closely the articulation afforded by a natural joint.